1. The Field of the Invention
This invention relates to an apparatus for converting coal, petroleum residue, tar sands and similar materials to hydrocarbon liquids or gases. The invention particularly relates to an advantageous reactor design that overcomes several reactor-associated performance problems and improves the overall efficiency of the conversion steps occurring in the reactor, particularly the catalytic hydrogenation and/or hydrocracking of coal particles into hydrocarbon liquids in catalytic slurry reactors.
2. The Relevant Technology
The conversion of fossil fuels such as coal, natural gas and peat to liquid hydrocarbon fuels and/or chemicals has been the subject of intensive research and development throughout the industrialized world for many years to provide a practical alternative to petroleum crude oil production and open-up the world's vast reserves of coal as a competitive source for essential hydrocarbons. Many processes have been developed for the direct or indirect catalytic hydrogenation of fossil fuels to yield liquid hydrocarbons; some large pilot plants have been built and operated, and about twenty commercial scale plants have been built for the conversion of coal to primarily liquid hydrocarbons. Of these twenty plants, most were built by the German government during World War II. They were built using the well-known Fischer-Tropsch (F-T) process for converting synthesis gas to liquid hydrocarbons in contact with iron catalyst and, operationally at least, worked well enough for war-time needs. Subsequently, the South African Government (SASOL) built two commercial-sized coal conversion plants to produce hydrocarbon fuels and chemicals which also were successfully based on indirect conversion using Fischer-Tropsch chemistry and iron catalysis. Both the German and SASOL projects were driven by political necessity but were otherwise commercially uncompetitive with crude oil discovery and production.
The F-T process is a known method for preparing liquid hydrocarbons from fossil fuels, especially coal, by conversion of coal to synthesis gas, i.e., a mixture of carbon monoxide and hydrogen, followed by conversion to liquid hydrocarbons over a precipitated iron F-T catalyst. However, precipitated iron catalysts in the F-T process are especially fragile and break down easily under conventional reaction conditions into very fine particles which are carried over into the hydrocarbon liquid products. U.S. Pat. Nos. 6,265,451 and 6,277,895, assigned to Hydrocarbon Technologies, Inc., and incorporated herein by reference in their entirety, teach skeletal iron F-T catalysts for the production of liquid hydrocarbons from fossil fuel derived synthesis gas in a slurry reactor. The patents teach and claim a relatively simple and inexpensive method for preparing the skeletal iron F-T catalyst that experiences less attrition and the conversion of syngas is higher than that obtained by using fused iron as catalyst. Also, the conversion of the feed is equivalent to that achieved by precipitated iron F-T catalyst. The catalyst is recycled in the process.
U.S. Pat. No. 6,190,542, also assigned to Hydrocarbon Technologies, Inc., teaches a multi-stage direct catalytic hydrogenation and hydroconversion process for the conversion of fossil fuels such as coal over iron catalysts to low boiling hydrocarbon liquid products. The first stage of the hydroconversion and hydrogenation process utilizes a backmixed reactor.
A catalytic reactor system that has been successfully used to directly convert coal or heavy hydrocarbon feedstock such as residuum and oils from tar sands into lighter hydrocarbon liquids is the ebullating bed reactor. In this reactor, upward flowing streams of coal fines, liquid and gaseous materials such as oil and hydrogen flow upward through a vessel containing a mass of solid catalyst particles. The mass of particles expand by at least 10% and are placed thereby in random motion within the vessel. The characteristics of the ebullated mass are such that a finer, lighter solid will pass upwardly through the mass of catalyst particles such the ebullated mass is retained in the reactor, and the finer, lighter material may pass from the reactor along with the lighter hydrocarbon liquid products. An exemplary ebullated bed reactor is described in U.S. Pat. Nos. 3,519,555 and 3,769,198 and is well known to those skilled in the art of petroleum residuum upgrading and coal conversion. It is employed in the H-Coal process as described in U.S. Pat. No. 4,400,263 and in the H-Oil process for the hydrotreating of residuum as described in U.S. Pat. No. 4,526,676. It can also be employed in the more advanced hydroconversion process, i.e., the catalytic multi-stage process, for the conversion and refining of a hydrocarbon feed as described in U.S. Pat. No. 6,190,542 where the catalyst is a dispersed catalyst and the catalyst is integral part of the feed to the reactor. The catalytic slurry bed reactor apparatus for coal or residuum conversion is typically operated at high hydrogen partial pressure between 2,000 and 3,500 psi at a reactor temperature between 700° F. and 850° F.
Processes dedicated to the hydrogenation and hydroconversion of seemingly intractable materials, such as coal and petroleum residuum, are routinely faced with the challenge of designing an apparatus that can contain catalytic particles at high pressures and temperature while converting an evenly distributed feed stream of hydrogen feed gas, hydrocarbon liquid and vapor and reactant particles; a liquid recycle stream of converted mixtures preferably must be made essentially free of vapor and pumped back to the reactor as a recycle feedstream; and a recycle flow return pump must assure that an even distribution of the recycle stream occurs across the bottom plenum of the reactor to avoid settling and coking of unreacted coal particles. Conventionally, and to a greater or lesser degree, these problems are overcome in the prior art by introducing the feedstream through a sparger and distribution plate which favors an even distribution of reactants across the reactor and using a reactor cup riser for liquid/vapor separation in the reactor. Improvements in the recycle return pump design and performance are also regularly sought.
The inventions described herein are directed to overcoming these and other problems encountered in apparatuses dedication to the hydroconversion of coal and/or heavy oil to produce lighter and more valuable hydrocarbon liquids.